Handle underlined and strikethrough attributes in wxGTK native font info.

Handle underlined and strikethrough attributes in wxGTK native font info.

These attributes were not handled by wxFont::GetNativeFontInfoDesc() as it
only serialized the Pango font description which doesn't support them.

Fix this by handling these attributes explicitly and prepending them to the
Pango font string if necessary.

Closes #14559.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72488 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775